Physics, Earth & Space
Cyclic Universe Can’t Avoid a Cosmic Beginning
This post was updated on August 25, 2022.
The recent flutter over whether the James Webb Space Telescope’s data stream is a plus or a minus for the Big Bang and the Standard Model of the universe touched on some interesting cosmological issues.
The Big Bang and the Standard Model support the assumption that our universe is finite and had a beginning. Could it have been eternal — with an infinite past instead of a beginning? The trouble is, when we try to apply concepts like infinity — typically used in mathematics — to the physical world, the basis of reality can collapse into absurdity.
The world science observes seems to be finite; time starts at a certain point, flows in one direction, and features some occurrences but not others at the same moment.
But there is another theory on offer, the cyclic universe: “The cyclic universe theory is a model of cosmic evolution according to which the universe undergoes endless cycles of expansion and cooling, each beginning with a ‘big bang’ and ending in a ‘big crunch’.” — McGraw-Hill Access Science
The author of the article that supplies the definition above, Princeton theoretical physicist Paul J. Steinhardt, also notes,
Although the cyclic model differs radically from the conventional big bang–inflationary picture in terms of the physical processes that shape the universe and the whole outlook on cosmic history, both theories match all current observations with the same degree of precision. However, the two pictures differ in their predictions of primordial gravitational waves and the fine-scale statistical distribution of matter; experiments over the next decade will test these predictions and determine which picture survives.PAUL J. STEINHARDT, “CYCLIC UNIVERSE THEORY” AT MCGRAW-HILL ACCESS SCIENCE (NOVEMBER 2019)
Which Will It Be?
So, both the Big Bang theory and the cyclic universes theory find support from current science observations. But new physics findings in those areas where their predictions differ will likely support one or the other better. The Big Bang is, of course, much better known in popular culture.
One well-known proponent of a type of cyclic cosmology is British cosmologist Roger Penrose who won the Nobel Prize for physics in 2020. His model does not include a contraction stage followed by a bounce. Instead, he proposes that a universe at the end of one cycle, after all stars have died and black holes have evaporated away, transitions into a new cycle initiated by a Big Bang-type event.
Theoretical physicist Sabine Hossenfelder is not a fan: “If the previous eon leaves information imprinted in the next one, then it isn’t obvious that the cycles repeat in the same way. Instead, I would think, they will generally end up with larger and larger fluctuations that will pass on larger and larger fluctuations to the next eon because that’s a positive feedback. If that was so, then Penrose would have to explain why we are in a universe that’s special for not having these huge fluctuations.” — “Will the Big Bang repeat?” (February 26, 2022)
There Was a Beginning
Astrophysicist Brian Koberlein notes, however, that a cyclic universe does not eliminate the need for a beginning:
Each universe has a cause, and it’s turtles all the way down. But a new study has found a flaw in this idea. The team looked at the mathematical structure of cyclic universe models within general relativity and found that all of them are geodesically past-incomplete. In other words, within the bounds of general relativity, you cannot trace a universe like ours back through an infinite cycle of universes. There may have been a vast number of universes before ours, but there must still have been a first universe.
So the cyclic universe model can provide a cause for our universe, but it only kicks the problem of beginnings down the road. Even if our universe wasn’t the first, some universe was.BRIAN KOBERLEIN, “EVEN A CYCLICAL UNIVERSE NEEDED TO COME FROM SOMEWHERE” AT UNIVERSE TODAY (AUGUST 11, 2022)
The authors of the paper he cites say explicitly that their critique doesn’t apply to Penrose’s specific model, which they plan to look at next, because in his model “the scale of each universe is infinitely larger than the cycle before.”
Read the rest at Mind Matters News, published by Discovery Institute’s Bradley Center for Natural and Artificial Intelligence.